Plumbeeze Water Test Gauges designed to measure and register water system pressure within a system. Ideal for recording the highest pressure reached to determine if a pressure reducing valve (P.R.V.) is required as well as to troubleshoot problems caused by thermal expansion or pressure spikes. Maximum pressure indicator needle can be reset by turning external knob counterclockwise. The hose connection allows for direct connection to a water heater drain valve or hose bibb.